It may be desired during certain medical procedures to alter anatomic structures, such as by penetrating, or injecting into said structures, by intentionally perforating through these structures or by ablating through them. Such alterations of structure can facilitate diagnostic or therapeutic procedures, but may be accompanied by risks of causing harm to the patient if the alteration occurs in a manner or location other than intended. For example, when many structures are adjacent to each other, and the intention of the medical practitioner is to alter a focal region of these structures, harm can come from unintentionally altering neighboring structures. Image guidance during procedures has the potential to minimize the risk and improve the efficacy of the desired procedure by allowing the medical practitioner to more accurately position and manipulate devices in relation to the anatomic structures of interest.
As an example of a procedure in which image-guided manipulation would be of potential value, we consider the process of crossing the atrial septum of the heart (see J Am Coll Cardiol. 2008; 51:2116-22. Emerging Applications for Transseptal Left Heart Catheterization Old Techniques for New Procedures. Babaliaros V C, Green J T, Lerakis S, Lloyd M, Block P C). The present invention can be adapted to facilitate transseptal access to the left atrium guided by forward-looking ultrasound imaging. Transseptal access is required for performance of a variety of interventional procedures, including repair and/or replacement of diseased mitral and aortic valves, occlusion of the left atrial appendage, ablation of electrical pathways in the left atrium, pulmonary veins and left ventricle for treatment of arrhythmias, repair of defects within the inter-atrial septum, repair of paravalvular leaks and implantation of a percutaneous left ventricular assist device.
Physicians who perform certain invasive cardiology procedures often use minimally invasive techniques to deliver devices from a vein to the right atrium. Once in the right atrium, a variety of catheters may be inserted from the right atrium, through the inter-atrial septum into the left atrium and/or left ventricle. The procedure of crossing the septum typically involves creating a hole within the fossa ovalis through which the device(s) are navigated. Conventionally, a physician uses a transseptal catheter and a long, curved needle for left atrial access from the venous system. The catheter, which is curved to facilitate access to a desired portion of the left-heart anatomy, includes a sheath and may include a separate dilator. The curved needle may be, for example, a stainless steel Brockenbrough curved needle or a trocar. After penetration of the septum with the needle, a wire may be inserted into the left atrial cavity and used as a rail for insertion of larger caliber specific therapeutic or diagnostic devices.
The fossa ovalis is located posterior and caudal to the aortic root, anterior to the free wall of the right atrium, superiorly and posteriorly to the ostium of the coronary sinus and well posterior of the tricuspid annulus and right atrial appendage. The fossa ovalis itself is approximately 2 cm in diameter and is bounded superiorly by a ridge known as the limbus.
Although puncture of the fossa ovalis itself is quite safe, the danger of the transseptal approach lies in the possibility that the needle and catheter will puncture an adjacent structure. Accurate localization of the fossa ovalis and correct positioning of the needle are crucial in order to avoid these structures. After transseptal puncture, the most important problem is to determine whether the tip of the needle is in the left atrium. The most common complication of the transseptal approach is inadvertent puncture of the wall of the heart or great vessels. Puncture can occur in the superior vena cava, free wall of the left or right atria, the left atrial appendage, or the aorta, and can lead to pericardial tamponade and death, (see Cathet Cardiovasc Diagn. 1988; 15(2):112-20; Development and application of transseptal left heart catheterization. Weiner R I, Maranhao V).
Traditionally, transseptal punctures have been guided by fluoroscopy (see Circulation, 1966 September; 34(3):391-9; Considerations regarding the technique for transseptal left heart catheterization, Ross J Jr) however this form of imaging does not accurately delineate the critical cardiac structures; specifically the fossa ovalis. The operator therefore has to rely on a variety of unreliable fluoroscopic landmarks to guide the puncture. Under fluoroscopic guidance, rates of life threatening complications up to 1.2% have been reported (see Cathet Cardiovasc Diagn. 1994 32 332, The technique and safety of transseptal left heart catheterization: the Massachusetts General Hospital experience with 1,279 procedures; Roelke M, Smith A J, Palacios I F; and Clin Cardiol. 1986; 9(1):21-6, Transseptal left heart catheterization: a review of 278 studies; Blomstrom-Lundqvist. Olsson S B, Varnauskas E). Transseptal puncture remains therefore a difficult procedure that is burdened by rare but serious, or even life-threatening complications (see J Invasive Cardiol. 2005 February; 17(2):71-2; Comment on: J. Invasive Cardiol. 2005 February; 17(2): 68-70, Another trick to improve the safety of transseptal puncture; Colombo A, Iakovou I.). Transesophageal and intracardiac echocardiography have been employed to image the septum and atrii, however they have several disadvantages. Transesophageal echocardiography (TEE) limits communication with the patient (as it may require the patient's sedation), and creates risks of esophageal bleeding, longer procedure times, and even inadequate location of the fossa ovalis in some cases (see Roelke CCD 1994 32 332; and Pacing Clin Electrophysiol. 1996 March; 19(3):272-81; Transesophageal echocardiographic guidance of transseptal left heart catheterization during radiofrequency ablation of left-sided accessory pathways in humans. Tucker K J, Curtis A B, Murphy J, Conti J B, Kazakis D J, Geiser E A, Conti C R). Intracardiac echocardiography (ICE) accurately images the fossa ovalis, however it is expensive, invasive and requires placement of an additional device within the heart during the procedure (see Chest. 1995 July; 108(1):104-8; Intracardiac ultrasound imaging during transseptal catheterization; Mitchel J F, Gillam L D, Sanzobrino B W, Hirst J A, McKay R G). ICE may also require an additional access site to the venous system so that the ICE device can be delivered to the right atrium. TEE and ICE are limited by difficulty in imaging the needle tip at the time of the puncture and following penetration, and challenge the operator to coordinate fluoroscopic and ultrasonic images that are acquired from different sources in real-time. Furthermore, most ICE systems are side-viewing and provide only 2D images.
Therefore, transseptal puncture is a complex procedure limited by difficulty in achieving accurate and simultaneous real-time imaging of the needle tip, fossa ovalis and the surrounding cardiac structures. Development of a device that couples forward-looking imaging with the tip of the transseptal catheter would greatly enhance the safety and simplicity of these procedures. Such a device would not only accurately localize the puncture site within the fossa ovalis prior to penetration, but would also confirm the exact localization of the wire tip within the left atrium before insertion of larger caliber devices (with more potential for trauma if inadvertantly placed into an incorrect anatomic space) over the wire.
Following successful transseptal puncture, a variety of subsequent procedures may be performed. Most current transseptal punctures in the U.S. are being performed for the purpose of electrophysiological procedures. Ablation of atrial fibrillation involves isolation of the pulmonary veins using radiofrequency energy (see Circulation 2000 102 2619; Circumferential radiofrequency ablation of pulmonary vein ostia: A new anatomic approach for curing atrial fibrillation; Pappone C, Rosanio S, Oreto G, Tocchi M, Gugliotta F, Vicedomini G, Salvati A, Dicandia C, Mazzone P, Santinelli V, Gulletta S, Chierchia S) or cryoablation. These interventions are associated with prolonged procedure times and high doses of x-ray radiation, primarily because of difficulty in visualizing the ablation targets under fluoroscopy (see Curr Probl Cardiol. 2006 May; 31(5):361-90; Ablation of atrial fibrillation; Riley M J, Marrouche N F). In addition to ablation for atrial fibrillation, transseptal puncture is routine for ablation of accessory pathways located along the mitral annular region, left atrial tachycardias and flutters, and less commonly for variants of atrioventricular nodal reentrant tachycardia. The transseptal route also provides a useful alternative to the retroaortic approach for ablation within the left ventricle and left ventricular outflow tract.
Imaging with intracardiac echocardiography has simplified these procedures (see J Cardiovasc Electrophysiol. 2002 October; 13(10):986-9; Use of intracardiac echocardiography for prediction of chronic pulmonary vein stenosis after ablation of atrial fibrillation; Saad E B, Cole C R, Marrouche N F, Dresing T J, Perez-Lugones A, Saliba W I, Schweikert R A, Klein A, Rodriguez L, Grimm R, Tchou P, Natale A.), however the above limitations apply. Closure of a patent foramen ovale may be enhanced by imaging from transesophageal or intracardiac echocardiography (see Heart. 2005 April; 91(4):444-8; Closure of patent foramen ovale: technique, pitfalls, complications, and follow up; Meier B.) however the same limitations apply. Emerging technologies such as minimally invasive mitral valve repair (see J Interv Cardiol. 2006 December; 19(6):547-51; Erratum in: J Interv Cardiol. 2007 February; 20(1):91; Comment in: J Interv Cardiol. 2006 December; 19(6):483-4; Percutaneous transcatheter repair for mitral regurgitation; Block P C) may again benefit from accurate imaging of the transseptal puncture and valvular intervention.
Other applications of image guided alteration of anatomic structures may include injecting or otherwise delivering an agent, such as cells and/or pharmacologic agents into a localized region. Accurate localization of stem cell delivery to damaged myocardium is another example of such an application. Yet another application of image guided alteration of anatomic structures is the delivery of energy, such as electrical energy for ablating tissue, such as radio-frequency (RF) energy. RF ablation can be used to control or prevent arrhythmias, and it can be used to facilitate puncturing or penetrating through tissue. Visualization prior to or during the application of RF energy can be helpful in ensuring that there is adequate contact between the tissue and the RF energy delivery device. Creation of artificial connections between separate fluid chambers involves the placement of prosthetic conduits, and may benefit from optimal forward-looking procedural guidance. Percutaneous construction of artificial coronary arterial-venous vascular conduits has been proposed as a substitute for traditional coronary bypass surgery for the treatment of ischemic heart disease (see Circulation. 2001 May; 103(21):2539-43. Percutaneous in situ coronary venous arterialization: report of the first human catheter-based coronary artery bypass. Oesterle S N, Reifart N, Hauptmann E, Hayase M, Yeung A C).